Computer display devices have been configured to function both as an input device and as a video output device. For example, computer display devices can be configured with touch surface mechanisms that allow users to enter user input data through a display surface. Sensors can detect when one or more objects contact a particular location on the display surface. A computer system can then perform some action in response to detecting the contact. For example, in response to detecting contact between an object and a display surface at a location corresponding to user-interface control, a computer system can perform some action associated with the user-interface control.